What are the special cases of recursive calls in Java functions?

Recursively calling the function itself causes the following special situations: excessive recursion and no clear termination condition. Parameters are passed incorrectly, resulting in incorrect results or infinite loops. Complex logic, difficult to manage status. Tail recursion makes recursion equivalent to loops by eliminating the risk of stack overflow. Practical cases include Fibonacci sequence and tree structure depth calculation.

Special cases of recursive calls in Java functions

Recursive calls is a process in which a function calls itself. In specific scenarios Very useful, but can sometimes cause problems.

Special cases

1. Excessive recursion

Excessive recursion means that the function continuously calls itself, causing stack overflow. This is usually caused by a lack of explicit termination conditions. For example:

public static int factorial(int n) {
    return factorial(n - 1); // 没有终止条件
}

2. Incorrect parameters

If the parameters passed to the recursive function are incorrect, it will lead to incorrect results or infinite loops. For example:

public static int fibonacci(int n) {
    if (n <= 0) {
        return 1;
    } else {
        return fibonacci(n - 2) + fibonacci(n - 3); // 参数错误
    }
}

3. Complex logic

The more complex the logic of a recursive function, the more difficult it is to manage its state. For example:

public static List<Integer> generatePartitions(int n) {
    List<List<Integer>> partitions = new ArrayList<>();
    for (int i = 1; i <= n; i++) {
        List<Integer> partition = new ArrayList<>();
        partition.add(i);
        partitions.addAll(generatePartitions(n - i, partition));
    }
    return partitions;
}

4. Tail recursion

Tail recursion is a special type of recursion in which the function call itself is the last action of the function call. To the Java compiler, tail recursion is indistinguishable from loops, eliminating the risk of stack overflow. For example:

public static int factorial(int n) {
    return factorialHelper(n, 1);
}

private static int factorialHelper(int n, int result) {
    if (n == 0) {
        return result;
    } else {
        return factorialHelper(n - 1, result * n);
    }
}

Practical case

Fibonacci sequence

Use recursion to calculate the Fibonacci sequence:

public static int fibonacci(int n) {
    if (n <= 1) {
        return 1;
    } else {
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
}

The depth of the tree structure

Use recursion to solve the depth of the tree structure:

public static int treeDepth(TreeNode root) {
    if (root == null) {
        return 0;
    } else {
        int leftDepth = treeDepth(root.left);
        int rightDepth = treeDepth(root.right);
        return Math.max(leftDepth, rightDepth) + 1;
    }
}

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